When the head is neither reading or writing data, it has a general practice for prevention of destruction of data recorded on a magnetic disk in a magnetic disk unit to move a head to a landing region located outside a data recording region on the disk and, stop the head there. Once the head is positioned outside the data region the actuator for supporting and moving the head is locked, so that the head will not enter into the data recording region even when an impact or vibration is applied from outside.
Since it is harder to make the disk float up at the inner part than at the outer part of the disk, the landing region is usually located at the inner-most part of a disk.
U.S. Pat. Nos. 4,647,997 and 4,692,829 disclose one device for moving the head to a non-recording region and locking the actuator arm. When the power supply is turned off in this device, the kinetic energy of the spinning disk and spindle is converted into electrical energy by operating the disk driving spindle motor as a generator. The electrical energy produced is supplied to the coil provided on an actuator, to move the actuator and the head to the landing region.
FIGS. 5A and 5B show the actuator returning and holding device of U.S. Pat. Nos. 4,647,997 and 4,692,829 which returns an actuator carrying a head to a landing region, when the head is not in use. Turning on switch 192 connects terminals A and B causing spindle motor 114, which drives a magnetic disk 116, to turn. The spinning disk 116 results in a wind in a definite direction inside a magnetic disk unit. A vane 170 is biased in the direction of S by a coil spring (not shown). The wind, however, causes vane 170 to rotate in the direction W, which allows latch finger 168 to separate from an actuator 132. In this way, the actuator 132 becomes free to move.
When power to the storage device is interrupted or when a power supply is turned off, switch 192 connects terminals A and C which connects voice coil 138 installed on the actuator 132 and the spindle motor 114. Due to inertia, the spindle motor 114 turns for a while after power has been interrupted. The turning of the spindle motor yields a counter-electromotive force. This counter-electromotive force induces current flow in the voice coil 138, causing the actuator 132 to rotate toward the center of disk 116. Consequently, head 130 carried by the tip of actuator 132 moves toward landing region 126 which is inside of the data recording region 122 on disk 116.
Since the counter-electromotive force decreases rapidly, it is impossible to move the head 130 to the landing region 126 using only the counter-electromotive force. As a result, the biasing force of flexible cable 182 is also used to move the actuator and the head to the landing region 126. When spindle motor 114 stops, the force of the wind on vane 170 weakens as well. The force of the coil spring (not shown) then causes latch finger 168 to come in contact with the actuator 132, to lock the actuator 132 in place (see FIG. 5B).
Published Japanese Examined Patent Application No. 63-48110 discloses a locking mechanism for holding a carriage at a definite position. Leakage fluxes produced by a magnetic circuit in a voice coil motor are used to attract a magnetic body mounted on the rear of the carriage.
Each of the devices mentioned has shortcomings. Among the shortcomings associated with the device shown in FIGS. 5A and 5B is that there is a possibility that the head 130 carried by the actuator 132 may not be moved to the landing region 126 after the power is shut off. Since the spindle motor's counter-electromotive force rapidly diminishes, the actuator 132 must be moved to the landing region 126 by the biasing force of the flexible cable 182. However, this biasing force gets smaller as the actuator 132 moves toward the inside of disk 116.
If the flexible cable 182 is made thicker so as to assure a biasing force sufficient to move the actuator and hold the actuator 132 inside the disk 116 or if the radius of the bow formed by the flexible cable 182 is made smaller, the force produced by the flexible cable 182 when the actuator is positioned at the outside of the disk 116, will become large, making the actuator 132 difficult to control.
The flexible cable 182 may also lose the biasing force as a result of repetitive bending in the seeking operation. Then the flexible cable 182 would no longer move the actuator nor hold the actuator 132 in place over the landing area 126. Current trends in disk drive products aggravate this result. Current trends are toward smaller disk drives with smaller enclosures. Smaller disk drives will require narrower flexible cables which produce smaller forces and which are more prone to repetitive stress.
Further, the biasing force of the flexible cable 182 tends to undergo changes as temperatures and moisture vary.
The locking mechanism disclosed by Published Examined Japanese Patent Application No. 63-48110 linearly moves the carriage which supports the head in motion to retract the carriage from the magnetic disk and, then, locks it. Among the problems associated with this locking mechanism is that it is impossible to reset the head to the landing region when the landing region is located inside the magnetic disk.
An object of the invention is to provide an actuator returning and holding device capable of returning a head carried by an actuator to a landing region and holding it over the region. Another object of the invention is to provide such a device using a smaller number of parts. Yet another object of the invention is to provide a device which requires no power consumption, even if the landing region is located near the center of the disk.
A further object of the invention is to provide an actuator returning and holding device in which the force an actuator receives, as it is moving through a data recording region of a disk, is nearly constant.